Radio communication system



Sept.- 9, 1941. R. w. HART 2,255,162

' RADIO COMMUNICATION SYSTEM Filed Jan 13, 1940 2 Sheets-Sheet l i/v'on on lfid/o 77-ansmiffer 44 O v H HUI/QC.

INVENTOR. li bbcrfn liyl/al/arl BY, V

ATTORNE' Sept. 9, 1941. R. w. HART 2,255,162

RADIO COMMUNICATION SYSTEM Filed Jan. 13, 1940 2 Sheets-Sheet 2 lll l Patented Sept. 9, 1941 UNITED \STATES PATENT-OFFICE RADIO COMMUNICATION SYSTEM Robert Winfield Hart, Lynn, Mass, assignor to Submarine Signal Company, Boston, .Mass., a a corporation of Maine Application January'13, 1940, Serial No.'313,7l3 p 2 Claims. (Cl. 177-341) The present inverition relates to a radio transmitting and receiving system and more particularly to an alarm signal system therefor, also called a selective ringing system.

In radio telephone communication systems where it is desired to attract the attention of any one of a plurality of receiving station from one or more central stations or where it is desired to it is necessary to have some form of selective call system. Such a system should make it possible to operate an alarm at any desiredione of a group of receiving stations without affecting .the alarms at other receiving stations and regardless of static or other interference conditions. The present invention provides an arrangement of this type.

The invention will best be understood from the following description taken in connection with the accompanying drawings in-which Fig. 1 is a schematic diagram of an alarm signal transmitting device operating in conjunction with a radio transmitter, and Fig. 2 is a schematic diagram of an alarm-operatingreceiving device which is apparatus arranged to respond to the particular" order of frequencies transmitted.

As shown in Fig. 1, the alarm signal transmitting apparatus comprises a series of sharply tuned vibrating reeds I, 2, 3 and 4. Each of these be able to call any station from any other station,

The contacts l'i to 20 24. The reeds are initially set into vibration by means of the cams 25yto 28 all of which are mounted on the shaft 29 which can be rotated by means of the knob 30. The cams in the initial position bear against the studs 3| to 34 mounted on the reeds. The projections on the cams thus tension the reeds in one direction. Further rotation of the cams then permits the reeds to swin back and-thereby momentarily to close the contacts- I! to 20, whereby the magnets 5 to! will be momentarily energized; attracting the reeds toward them and thereby breaking the contacts ii to .20. The magnets are therefore again deenergized-and the reeds return to the right again, closing the contacts. Vibration of the reeds is thereby continued untll'stopped by rotation of projections again contact the cams so. that their the studs 3| to.

The rate at which the several reeds vibrate and therefore the rate at which their respective contacts are opened and closed is in each case determined by the natural frequency of the reeds. As above stated, the frequencies of the several reeds are different and are preferably chosen in the low audio frequency range, but other frequencies may be used if desired. Each reed can readily be adjusted to vibrate 'at precisely the correct frequency by adjustment of the position of the endweights 3G to 39.

are also each in series with a circuit which includes the operating coil 40 of an electromagnet 4| which operates the transmitter keying relay 42. The contacts 43 of this relay are preferably normally closed and are .35 opened when the magnet 4| is energized. The

relay coil 40 has one side'connected by the lead 44 to one side of the direct current supply. The other side of the coil 40 is connected by parallel paths to the keys 45 to 48, the other side of each 40 key being connected to one of the reeds and reeds is tuned to different low frequencies, for

example, 25, 30, and cycles per second, respectively. Vibration of the reeds is maintained by electromagnets 5 to 8, respectively, which are provided with windings 9 to l2. These are connected in parallel to one side of a-direct current source through current limiting resistors l3 to It. The other ends of'the windings 9 to I! are connected to the respective reeds I to 4, the circuit to the other side of the direct current simply being contemplated through contacts IT. to 20, each of which isclosed "once during each cycle.

impulse will be interrupted at the same freof vibration of the reed to which one of the contacts is attached. The contacts I? to 2d are shunted by spark-suppressing condensers 85 to thence through the reed contacts to the second side of the direct current line. Thus when the 'key' 45 is closed, the relay coil 40 will receive momentary energization each time the contact i l of the reed i closes. relay is therefore opened at the frequency of vibration of the reed i, for example 25 times a second." The radio transmitter is therefore keyed at this frequency and the resulting radio signal quency. The length of the impulse is controlled by the time during wh'ch the key G5 is depressed. Similarly, impulses of other frequencies can be transmitted by closing any one of the other keys 46,4? or 58. In practice it will usually be found Contact 43 of the keyine' tuned, While the arrangement shown operates .to interrupt the radio frequency carrier at the reed frequencies, it will be understood that, if desired, modulation of the carrier may be used instead.

The alarm-operating equipment for the receiving stations is shown schematically in Fig. 2. Alarm signal impulses received by the antenna 50 are passed through the 'detector 5| :and the low'frequency amplifier 52 from which they are supplied to the operating coils 53 to 56 of sharply tuned vibrating reed relays 51 to 60. These may be substantially similar to the transmitting reeds shown in Fig. 1 but they must be capable of automatically commencing vibration when energized at the proper frequency. As shown in the drawings the several coils 53 to 56 are connected in series so that all'the received signals pass through all of the coils. The vibrating reeds 6! to 84 are, however, sharply tuned so that none will vibrate unless the current passing through its operating coils very closely corresponds to the reeds natural frequency. Each reed connects with one or the other of a pair of parallelly connected contacts 85 to 68, respectively, thereby closing twice in each vibration of the reed a circuit containing the battery69. Each of the reeds 6| to 64 controls a relay II to I4, respectively, having the Vibration of the reed 8!, therefore, only eflects operation of the relay 12 if at the time the contacts IIB are closed. If this is the case, the coil I8 will be energized by vibration of the reed 82, thereby operating the relay I2 to close contacts 12A and 12B and to open contacts 120. The opening of contact 120 opens the holding current circuit for coil I5 of relay "II, thereby deenergizing the same and causing relay 1| to assume its normal condition.

The closing of contact 12A closes a holding current circuit which includes normally closed contact 13C and thereby maintains the relay I2 in an operated condition even after the reed 82 ceases to vibrate. The closing of contact 12B prepares the circuit including the operating coil II of relay I3 for operation upon the vibration of the reed 63. If this occurs, the operation of operating coils 15 to I8, respectively. Relay 1| is provided with two normally open contacts HA and I IB. Relay I2 is similarly provided with two normally open contacts 12A and 12B and a normally closed contact 120. Relays I3 and I4 are similar to relay having two normally open and one normally closed contact, namely 13A to 13C and MA to "C. In series with the operating coils I5 to II of the relays 'II to I3 there arethe normally closed contacts I9 to 8|, respectively, of thermal time delay relays 82 to 84, respectively, which are provided with operating heaters 85 to 81.

The several relay contacts are arranged in such a way that the relays cannot operate until the contacts of the preceding relay have operated.

Operation of the final relay operates the alarm 88 which may be energized by a battery 89. This takes place in the following manner. The relay coil I5 which is connected in series with the contact I9 is energized from the battery 89 by vibration of the reed 6| which closes contacts 65. Energization of coil I5 closes contacts HA and NB. Contacts IIA are in series with the normally closed contacts 120, the coil 15, contacts I9, battery 69 and heater coil 85 of the thermal relay 82. Thereis thus provided a direct battery connection which maintains the coil I5 energized and the relay Ii in operated condition when the contacts 'IIA are closed. The relay II will, therefore, remain in operative condition even after the reed 6| ceases to vibrate. However, the holding current for the coil I5 must pass through the thermal relay heater coil 85, causing a heating of the thermal elements in the relay 82 and, after a time, opening of the contacts I8.

The operating coil I8 of relay I2 is in a similar manner first energized by vibration of the reed 82 which periodically closes contact 88. Thecoil I8 is, however, not directly connected to the battery through the contact 68 but it is connected in series with the contact MB of the relay Ii.

relay I3 opens the holding current circuit to relay I2 at 13C, closes its own-holding'current circuit at 13A and prepares, byiclosing of contact 13B, the relay I4 for operationby vibration of the reed 84. In a similar manner vibration of the reed 84 by energizing coil I8 of relay ,I4 interrupts the holding current circuit ofrelay l3 and closes its own holding-current circuit at 14A. The closing of contact 14B serves to close the circuit to the alarm 88. The holding current circuit for coil .18 can be. interrupted only by pressing the alarm release key 90. This deenergizes the relay coil 18 and thereby stops the alarm.

From the aboveit will be evident that the alarm can be operated only if the reeds; 8| to 64 are vibrated successively. Since these reeds are tuned to different frequencies, they will operate successively only if signal impulses of the corresponding frequencies are successively received in the proper order. For example, if any other frequency than that corresponding. to reed 6i be received first, nothing at all will happen, for none of the relays II to I4 can operate unless the preceding relay has been operated. As a further example, if it be supposedthat an impulse of frequency corresponding to reed 6i was duly received, thereby operating relay II nothing further will happen if the following signal has a frequency other than that of, reed 62. If, for example, the following signal had the frequency of reed 83, this reed would vibrate closing'contact 61 but the relay coil I'I would not be energized since the contact 123 of relay I2 would still be open. Consequently this signal Lwould have no effect. Moreover, in a short timelafter the initial operation of reed 6i the ;thermal relay-82 would operate to open relay. H, so that'even though the third signal corresponded in frequency to the reed 62, the alarm still would not be operated. The time of delay prior to the opening of the thermal relay must, of course, be chosen as less than the time required to transmit twosuccesslve signal impulses.

Each transmitting and calling station is provided with the low frequency impulse transmitting equipment shown in Fig. 1 and each receiving station is equipped with an alarm system as shown in Fig. 2. Both transmitting and receiving systems contain the same number of tuned reeds of the same frequencies. In the several receiving stations, however, the order in which the frequencies of the reeds is arranged is dii'- tively varying in frequency in accordance with the frequency arrangement of the tuned reeds at the receiving station which is being called. Any desired order of frequencies can be used to designate a receiving station except that the same frequency cannot be used successively although it may be used alternately with one other frequency. Thus, although it has been stated that the four consecutive signal impulses transmitted to call a particular receiving station must be of different frequency, it should be noted that they need only be consecutively different in order to provide complete selectivity. Most receiving stations will have their four reeds all tuned differently, but some may have alternate reeds tuned to the same frequency. In this way by providing four differently tuned reeds at each transmitter it is possible to call 108 different re ceiving stations selectively. By increasing the number of differently tuned reeds in the transmitters to five and increasing the receiving reeds and accompanying relays at the receiving stations to five, it is possible to call selectively any one of 1280 receiving stations. Still more reeds can, of course, be used if necessary.

. The present invention not only provides an efficient selective radio alarm system but also one which is not subject to erroneous and false alarms on account of static or other radio interference. This arises out of the use of tuned reeds which can readily be adjusted to require the continuance of the low frequency signal of proper frequency for a period of several seconds before engaging their respective contacts. It is seldom to be expected, therefore, that static or other radio interference will provide impulses of precisely the right frequency for a long enough 4 period of time to actuate any of the receiving reeds with a larg enough amplitude to cause them to close their contacts.

Having now described my invention, 1' claim:

1. An alarm signal receivingsystem for selective response to a code of a plurality of successive signal impulses of successively different frequencies arranged in a predetermined order comprising a plurality of relay circuits corresponding to the number of signal impulses in said code, each circuit containing a resonant vibratory reed relay tuned to one of the frequencies in said code, second relay means in each of said circuits adapted to be operated by the respective reed relays, contacts in said relay means, a power source, a plurality of time-delay devices and circuit connections between said elements and between said circuits for maintaining said second relay means closed after said reed relays cease to operate, for subsequently opening each of said second relay means a predetermined time after its first closing and for preventing the operation of any of said second relay means except while the second relay means in the pre-,

ceding circuit is closed and alarm means in the last of said circuits, whereby the alarm is oper ated only after receipt-of said different frequency impulses in said predetermined order.

2. An alarm signal receiving system for selective response to a code of successive signal impulses of successively different frequencies arranged in a predetermined order comprising a plurality of relay circuits corresponding in number to the number of signal impulses in said code, each circuit including a resonant vibratory reed relay tuned to one of the frequencies in said code and having contacts adapted to be closed by the vibration of the reed upon energization of the relay by a signal of the respective frequency and a locking relay having an operating coil and first and second normally open contacts adapted to be closed when the relay coil is energized and said locking relays in each circuit except the first having third contacts normally closed and adapted to be opened when the relay coil is energized, the several relay circuits being arranged with the tuned reeds in the order of the frequencies of the code to which response is desired, a power source, a plurality of timedelay devices, one for at least all but the last of said relay circuits, said time-delay devices having operating coils and normally closed contacts adapted to be opened a predetermined time-interval after the beginning of current flow through them, means connecting said reed-relay contacts, power source and time-delay device contacts of each circuit in series and in each circuit except the first also in series with said second contacts of the holding relay in the next preceding circuit, means connecting said power source, first locking relay contacts, locking relay operating coil and time-delay device operating coil of each circuit together in series and in each circuit except the last also in series with said third contacts of the locking, relay in the next'following circuit, alarm means in the last of said circuits and means for operating the alarm in response to operation of the locking relay in said last relay circuit.

ROBERT WINFIELD HART. 

